2025/11/19 by Bangaru, Haripriya, Calderini, Giovanni, Dannheim, Dominik +5
Engineering · Materials Science · #3D IC and TSV technologies #Copper Interconnects and Reliability #Electronic Packaging and Soldering Technologies #FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #Instrumentation and Detectors (physics.ins-det)
paper · doi:10.48550/arxiv.2511.15562
openalex publication_date 2025/11/19 · openalex created_date 2025/11/23 · openalex updated_date 2026/07/28
Fine-pitch hybridisation processes are essential for next-generation pixel detectors and high-density microelectronic assemblies. Conventional bump-bonding techniques, although reliable, remain costly and difficult to implement for single-die applications. In this work, we present flip-chip hybridisation results combining Electroless Nickel Immersion Gold (ENIG) bumping with Anisotropic Conductive Film (ACF) bonding, both developed in-house. This method enables fine-pitch interconnections without requiring wafer-level processing. The feasibility of the ENIG-ACF process for functional devices was demonstrated by hybridising functional Timepix3 ASIC and Ti-LGAD (Trench Isolated Low-Gain Avalanche Detector) sensors with 55 um pitch. The approach was then extended to test structures with 25 um pitch, using aligned-particle ACFs. The analysis revealed that the main limitation originated from the mismatch between ACF thickness and bump height, underlining the importance of interface geometry optimisation. To address this, a dedicated simulation program was developed to model the isotropic growth of ENIG bumps and to determine the optimum bump height as a function of ACF thickness and pixel-matrix geometry. The results provide valuable guidelines for future high connection density assemblies and demonstrate the potential of the ENIG-ACF process as a scalable, low-cost alternative to conventional bump-bonding techniques.